Time delay device



May 10, 1932. E. FOUCAULT TIME DELAY D EhcE Filed March 14, 1930 Inventor v Edouard Fouc'au 5 H is Attofn e B meats 10, 1932 UNITE [STATES 'ATENT OFFICE nnou'snn noucaunr, or rams, FRANCE, assrenon r GENERAL nLnc'rnIc comm,

A CORPORATION on NEW YORK TIME DELAY DEVICE Application filed March 14, 1930, Serial No. 435,890, and in France August 28, 1989.

' The invention relates to time delay devices, particularly those involving an electrically heated thermal operating element and has for its objectto render such devices more quicklycapable of repeating their timing.

operations.

For. actuating time delay devices it has been customary to use an element, ordinarily of the bi-metallic type, the deformation of -which under the efiect of variations in its temperature brought about by a suitable heat source accomplishes the closing or opening of an electric contact orperforms other 0 erations such as the turning of a valve. 11 order to simplify the description of the present invention, reference will be made par- 'ticularly to electric relayswhicli are intend-- ed to insure the closing of an electric contact with .a time delay. However, the invention can'be applied also to relays. that are intended for other purposes and which are deferred by the action ofan element which is deformable by dilation but which may not be a bi-metallic contact. 1

Thetime delay relays of the kind conand of moderate price for. the reason t at they do not comprise any special mechanism, particularly no electromagnets. Moreover, the variations in the control potential have little influence 0n-1the time settin However, these relays in certain applications have a considerable -sho rtcoming; When the bi! metallicf o crating element, after having 1 been suitaly heated, has attained such a deformation that'thedesired electriccontact I is established, this contact lasts for' a rather longtimeeven if the heating should be stopped shortl after it is established. This is because oft e;;.natural slowness of cooling of the bi..-n eta1lic'e1ement-.' The result is that ifLonewishe's'tO repeat the operation before the-element'.coo1s',one will not get the, re-

tarded'funcfioningwhich is wanted but inel steadinstantaneous"operation.

.sidered have the advantage'of being sim 1e Particularly when such apparatus is used as an accelerating relay in an automatic starter for the contactors of an electric motor, there is the possibility that in the case of two consecutive operations the second starting will proceed under abnormal conditions. Because of this severedisadvantage, this thermal time delay system is not ordinarily used foraccelerating purposes.

The present invention provides an improved deferred-action relay with a'thermostatic element which avoids the short-comings just -mentioned. It is characterized principally by the fact that its deformable element consists of two parts, one main part which is affected by the heat source and which becomes deformed in a proper direction for the operation which the'relay-must perform,

and a second part which is an extension of the main part which is heated only three h conductivity by that main part and W ich is deformed in the opposite direction.

The construction and operation of a pre ferred form of thermal time delay relay em-. bodying the invention can be best understood by referring to the accompanying drawings in which Fig. l is a schematic diagram of a thermal time delay relay conforming to the invention, Fig. 2 is a. chart showing typical time displacement characteristics of such a device, Figs. 3- and 4 are respectively side .and front views of a preferred construction of a relay embodying the invention, and Fig. 5 is a circuit diagram illustrating the manner of applying the thermal timedelay relay to an. automatic star-delta starter for electric motors. i

. In accordance with the present invention, the thermostatic element consists of two bimetallic elementsiAB and AC which are so assembled and joined together at A that,

under the effect of the heat, the lower bi- The heating element which is represented by an electric resistance is associated with t e lower bi-metallic contact AB and its terminals are D and E. The upper end of the element AC can engage with a micrometric screw F which closes the circuit GH, this closing representing here the desired operation. The thermostatic element isv reached by the heatconducted thereto from the strip AB.

Thus contact FC becomes closed in position II of the thermostatic element which is shown as a thin line in the drawings while thestarting position is shown as a heavy line.

At this moment (or in general when one wishes to bring the relay to the rest position), the circuit of the heating apparatus is interrupted by an auxiliary contact of the apparatus which is controlled by the relay-and the lower strip AB begins to cool. 1

If the cooling'took place only by conductivity through the surrounding air, it would be very slow and the end G of the thermostatic element would remain for a long time in contact with screw F just as it happens in the relays that are known at present. But, because of conductivity, a certainquantity of heat goes from.the lower strip AB to the upper strip AC. Under this influence this strip is curved to the right according to the dot-and-dash line of position III, and interrupts in this manner the contact FC. As soon as the time required for this displacement'has lapsed, the operation can be repeated and, if the thermostatic element is, for p in position III, one will not have instance,

such a long delay as if one were starting from the cold element, but there will always be a delay, whereas without this arrangement,no time delay would be possible if .the

' operation were repeated after the same only a very short time which can be adjusted.

at will. 4

To this end one must examine the ratioperiod of time. I

' It is possible to judiciously combine the heating conditions of each one of the two bimetallic contacts sothat the position II lasts which exists between the displacements of point C and the heating conditions of the thermostatic element.

The displacement of point C, which is intended to come in contact with screw'F. is the result of the displacements of A with respect MB and of C with respect to A. These ism two displacements are of, the same nature and are both due to the deformation of the bimetallic contact under the effect of the heat. The law according to which point A moves with respect to B is given by the curve (13 of Fig. 2, in which the times are plotte as abscissas and the dis lacements-measured' at right angles to B when the latter is in the rest p0siti0nare plotted as ordinates. The heating period lasts from o to b. During the interval 0 to a the heat which is produced serves simply-to heat the heating ele ment itself and no heat oes over to the bimetallic contact which indicates a time of rest. At (2 a balance or steady state position has been attained for a given power in the heating elementand any continued heatingv at the same regime would not modify this deformation.

Let us assume that the heating is stopped at this point. During the time be the cat ing element which is hotter than the strip AB ields still a sufficient amount of heatto the atter to balance the losses by conductivity through the air and the point A, at which the two strips meet, indicates the time of rest.

Then at 0 the cooling begins, according to a.

law, which is .much slower than the law which controls the heating.

Assuming that the part AC of the thermostatic element be indeformable and that the starting distance 3 (see Fig. 1) has been adjusted to the value e7, the operation, according to curve (1), gives a time delay T and a minimum waitlng t during which the contact FC remains closed.

If, without modifying the heating system,

one regulate to a valve 6 which is much lower than the balance deformation, and one ceases to apply heat at point 9, one obtains the curve (2) which gives the time delay T shorter than T and the minimum waiting time which is much longer than t Curve (3) refers to the displacement of oint C with respect to A, under the influence of the heat from the heating element, which also passes, through conductivity,

from stri \AB to strip AC. It is a curve similar but of less amplitude (since the heating is not direct) and'with a longer initial time of rest oa since the heat goes over into strip.

AC'only after a certain time following the heating of strip AB.

The resultant of the two displacements (2 and 3) is the curve (4) which represents the One willrea'lize' absolute motion of point C.

that with the regulation of y to the value e one obtains thes'ame delay T as above but a reduction of the minimum waiting time'tot, which is much smaller than t This brings outclearly the advantage of the new relay.

In order to reduce the time t to its mini-- mum value, curve (2) being given, one must modify the amplitude and time displacement of curve (3). This'is obtained by varying Figs. 3 and 4 represent schematically a physical embodiment of a relay which conorms to the invention, where the heating is assured b a heating element involving the alent to those of Figs. 3 and 4 may be used J oulian e ect. Fig. 3 is a side view and Fig. 4. is a front-view, the notation having the same meaning as inFig. 1. It goes'without saying that any arrangement which is equivwithout going beyond the scope of the invention.

The latter is of general application, no matter what operation is to be performed by the relay, and how the latter isheated. Fig.

5 shows a schematic view of an application to the automatic control of a star-delta switch for the stator winding of an induction motor, the change-over having to take place after a given time following the a pllcation of voltage to the motor so as to re in current.

- The particular motor control arrangements that are described with respect to this '3 example must be considered as constituting part of the invention and it goes without saymg that all other equivalents may be used vwithout leaving the scope of the invention.

The stator element of the motor is represented schematically: by the three phase i -13 -13, S, the rotor is not shown for the sake of simpliclty) which may be supplied through a threeole breaker J.

' The star-delta switc is operated by an 40- electro-magnet ET which, when it is enerzed, controls at the terminals of two phases F and E through the closin of contact R, the opening of the contacts S a, and S S as well as the closing of contacts S E -S E and E 8;, 2. TlllS device can be built, for

mostatic relay (see Fig. 1), the heating eleinstance, according to Fig. 1 in the French patent application that was filed May 18, 1928, by the Compagnie Francaise pour lExploltation des Procedes Thomson-Hous- 50 ton foran automatic starter for alternating-current motors or according to any other arrangement. 7

Contact R consists, in conformity with the invention, of terminals G. and H of a Itherment K of which, in series with the resistance r, is connected between phase and neutral to ward the load end of breaker J.

In the rest position contacts S S and S S,

are normally closed and the contacts S E;,

SE E 1 S 2 and R are open. 5

By closing breaker J, the stator winding ofthe motor being star-connected. the motor will start, and voltageis applied to a heat- 'ing element K.

uce the start '7 when the time interval, forwhich the bimetallic contact relay is set, has elapsed, this 'relay operates by closing its contact R. The

tact E S 2 accom lishes the energization of electr'omagnet E and the contact E 8, short-circuits the heating element of the relay which begins to cool, as has been explained in'the preceding. The contact'R opens which permits of proceeding anew with a repeated starting under favorable conditions.

With the bi-metallic contact relays that are known at present there is a possibility that, if one wishes tohave a second starting shortly after the first, contact B may still be closed andlthis would occasion a direct delta starting. This danger is avoided by applyingr the invention.

he delay which is obtained by this relay system varies slightly with the potential of the network. One may widely reduce its variations by providing the resistance r with a sufiiciently high temperature coeiiicient. \Vhat I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermal responsive device having oppositely acting portions in heat conducting relation and means for heating only one of said portions to efiect operation of the device metallic elements in heat conducting relation,

means: jointly controlled thereby, and electrical means for heating, only one of said elements to efi'ect operation of the means jointly controlledthereby a desired interval after the heating means is energized and insure a reverse operation of said controlled means before said one element is cooled when the heating means is deenergized.

4.- In combination, a heat responsive element having one. portion fixed and. another portion movable, an oppositely acting heat respensive element mounted'on said movable portipn of the firstfelement in heat conducting-relation therewith, a member movable between two positions under the joint control of said elements, and heating means associated with only one of the elenientsto insure a quick reverse movement of the memher by the other elementwhen the heating is sto pad.

5. fn combination, a bimetallic element having one end fixed, an oppositely acting bi-metallic element having one end secure in heat conducting relation with the free end of the first element, and heating means associated with only one of the elements to insure a quick reverse movement of the free end of the said oppositely acting element when the heating is stolpfied.

In witness whereof ave hereto set my hand this 13th day of February, 1930.

EDOUARD FOUOAULT. 

